Lithography techniques include processes in which, for example, a resist film formed from a resist material is formed on top of a substrate, the resist film is selectively exposed with irradiation such as light, an electron beam or the like through a mask in which a predetermined pattern has been formed, and then a developing treatment is conducted, thereby forming a resist pattern of the prescribed shape in the resist film.
For miniaturization of semiconductor devices, shortening of the wavelength of the exposure light source, and increasing of the numerical aperture (NA) of the projector lens have progressed. Currently, exposure apparatuses in which an ArF excimer laser having a wavelength of 193 nm is used as an exposure light source and NA=0.84 have been developed. As shortening the wavelength of the exposure light source progresses, it is required to improve various lithography properties of the resist material, such as the sensitivity to the exposure light source and a resolution capable of reproducing patterns of minute dimensions. As resist materials which fulfill the aforementioned requirements, there is used a chemically-amplified resist containing a base resin that displays changed solubility in an alkali developing solution under action of an acid, and an acid generator that generates an acid upon exposure.
Resins (acrylic resins) that contain structural units derived from (meth)acrylate esters within the main chain are now widely used as base resins for chemically-amplified resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm.
Here, the term “(meth)acrylic acid” is a generic term that includes either or both of the acrylic acid having a hydrogen atom bonded to the α-position and the methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of an acrylate ester having a hydrogen atom bonded to the α-position and a methacrlyate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of an acrylate having a hydrogen atom bonded to the α-position and a methacrylate having a methyl group bonded to the α-position.
As a technique for further improving the resolution, a lithography method called liquid immersion lithography (hereinafter, frequently referred to as “immersion exposure”) is known in which exposure (immersion exposure) is conducted in a state where the region between the objective lens of an exposure apparatus and the resist layer formed on a wafer is filled with a solvent (immersion solvent) that has a larger refractive index than the refractive index of air (see for example, Non-Patent Document 1).
According to this type of immersion exposure, it is considered that even if an exposure light source with the same wavelength as those conventionally used is used, high resolution equivalent to the resolution obtained by using an exposure light source with a shorter wavelength or by using a larger NA lens can be obtained, with no lowering of the depth of focus. Furthermore, immersion exposure can be conducted using a conventional exposure apparatus. As a result, it is expected that immersion exposure will enable the formation of resist patterns of high resolution and superior depth of focus at lower costs. Accordingly, in the production of semiconductor devices, which requires enormous capital investment, immersion exposure is attracting considerable attention as a method that offers significant potential to the semiconductor industry, both in terms of cost and in terms of lithography properties such as resolution.
Immersion exposure is effective in forming patterns having various shapes. Further, immersion exposure is expected to be capable of being used in combination with currently studied super-resolution techniques, such as phase shift method and modified illumination method. Currently, as the immersion exposure technique, a technique using an ArF excimer laser as an exposure source is being actively studied, and water is mainly used as the immersion solvent.
In recent years, fluorine-containing compounds have been attracting attention for their properties such as water repellency and transparency, and active research and development of fluorine-containing compounds have been conducted in various fields. For example, in the field of resist materials, currently, an acid-labile group such as a methoxymethyl group, tert-butyl group or tert-butoxycarbonyl group is being introduced into a fluorine-containing polymeric compound, in order that the fluorine-containing polymeric compound is used as a base resin for a chemically-amplified positive resist. However, when such a fluorine-containing polymeric compound is used as a base resin for a chemically-amplified positive resist, a disadvantage is caused in that, for example, a large amount of gas (out-gas) is generated after exposure, and the resistance against dry-etching gas (etching resistance) is unsatisfactory.
Recently, as a fluorine-containing polymeric compound exhibiting excellent etching resistance, a fluorine-containing polymeric compound having an acid-labile group containing a cyclic hydrocarbon group has been reported (see, for example, Non-Patent Document 2).
[Non-Patent Document 1] Proceedings of SPIE, Vol. 5754, pp. 119-128 (2005).
[Non-Patent Document 2] Proceedings of SPIE, Vol. 4690, pp. 76-83 (2002).